History:
"Many centuries ago, three carefully-selected young Earthlings were
transported from their native lands to my faraway world. Here they were granted
astounding powers, and eternal youth, then returned to Earth, their mission
to watch over the human race, helping the good in it to survive and flourish.
In the course of history, their names have become legend:

Hercules, empowered with the strength of a hundred men; Astrea, able to assume
any living form; Mercury, the amazing athlete who can match the speed of
light.

Working together with me, Sentinel One, and my maintenance robot, Mo, these
teenage guardians form the greatest team the world has ever known: the Space
Sentinels."

The
three heroes so chosen now live in a spaceship hidden in an inactive volcano
(possibly next door to Birdman's volcano
base!), having no civilian identities to return to between missions. They
take instruction from Sentinel One, who appears as a holographic face floating
in mid-air (like Zordon in the Power Rangers!). The base maintenance is carried
out by M.O. (Maintenance Operator), a small robot who has a crush on Astrea
(presumably he keeps in touch with 7-Zark-7 and Alpha 5, other annoying
robots who maintain G-Force and the Power Rangers bases respectively). Among
the team's many opponents is Sentinel-turned-bad Morpheus.

Comments:
Originally titled The Young Sentinels before being renamed mid-way through
the season as The Space Sentinels, the show ran a total of thirteen episodes,
each twenty minutes long. Produced by Filmation, it aired on NBC in 1977.
The thirteen episodes were:

Morpheus: The Sinister Sentinel

The Time Traveler

Space Giants

The Return of Anubis

The Prime Sentinel

Loki

The Sorceress

The Wizard of Od

Fauna

The Jupiter Spore

Voyage to the Inner World

The Test

The Worldship

Sentinel One was voiced by George DiCenzo (who also provided the voice for
Hercules), while Mo was voiced by Ross Hagen.

After the show ended, Hercules joined a new team for a while - Freedom Force.

Powers/Abilities:
Hercules is superhumanly strong, to an undefined degree. He can also fly,
and does not age. He later acquired a winged horse during his time with Freedom
Force, although it isn't clear if this means he had lost his ability to fly
at the time.

History: (Young Sentinels/Space Sentinels) Hercules was kidnapped
as a youth and taken by aliens to another world where he, and others like
him, where trained and given special powers, before being returned to his
homeworld to watch over the well-being of his people, as part of a group
of Sentinels.

(Freedom Force) Hercules was recruited to be part of Isis'
Freedom Force. I don't know if he had left the Sentinels, or was just juggling
both jobs.

Comments: Hercules was voiced by George DiCenzo in the Space Sentinels
cartoon and Bob Denison in the Freedom Force cartoon.

Astrea

Real
Name: Unknown

Identity/Class: Human mutate

Occupation: Protector of mankind

Affiliations: The Space Sentinels

Enemies: Morpheus

Known Relatives: None known

Aliases:
None known

First Appearance: The Young Sentinels (Filmation for NBC, 1977)

Powers/Abilities: Astrea can transform into virtually any animal at
will. She is also able to fly, and does not age.

History: Astrea was kidnapped as a youth and taken by aliens to another
world where she, and others like her, where trained and given special powers,
before being returned to her homeworld to watch over the well-being of his
people, as part of a group of Sentinels.

Comments: Astrea was voiced by Dee Timberlake

Mercury

Real Name: Unknown

Identity/Class: Human mutate

Occupation: Protector of mankind

Affiliations: The Space Sentinels

Enemies: Morpheus

Known Relatives: None known

Aliases: None known

First
Appearance: The Young Sentinels (Filmation for NBC, 1977)

Powers/Abilities: Mercury is superhumanly fast, capable of moving
at hundreds of miles an hour. He can also fly, and does not age.

History: Mercury was kidnapped as a youth and taken by aliens to another
world where he, and others like him, where trained and given special powers,
before being returned to his homeworld to watch over the well-being of his
people, as part of a group of Sentinels.